In the present commercial petroleum refinery techniques, hydrocarbon streams are obtained which are quite complex and contain terminal or alpha olefins and internal olefins. The alpha olefins are far more valuable than the internal olefins. While most such streams contain predominantly alpha olefins, the olefin mixtures also contain undesired amounts of internal olefins. The use of conventional means for purifying alpha olefins such as, for example, distillation results in a decreased amount of internal olefin contaminants, but still leaves a relatively large amount of internal oldefins in the alpha olefin feed. Purification of of alpha olefins contaminated with internal olefins of the same carbon number is particularly difficult. Hence, a process whereby the alpha olefins are purified of internal olefin contaminants would be quite useful.
It is known from U.S. Pat. No. 3,647,906, issued Mar. 7, 1972, to produce alpha olefins by reacting internal olefins and ethylene (i.e., ethenolysis) with a Re.sub.2 O.sub.7 -on-alumina catalyst at 140.degree. C. However, the purities or selectivities to alpha olefins were not reported. In U.S. Pat. No. 3,658,927, issued Apr. 25, 1972 and Journal of Catalysis, 7, 269-276 (1967), a heterogeneous molybdenum oxide catalyst at high temperature was used for ethenolysis. The reaction produced alpha olefin with either low conversion or low selectivity.
In addition, a variety of catalysts have been employed for conducting disproportionation (ethenolysis) type reactions, such as those disclosed in U.S. Pat. No. 3,340,322, issued Sept. 5, 1967; U.S. Pat. No. 3,637,892, issued Jan. 25, 1972; U.S. Pat. No. 3,760,026, issued Sept. 18, 1973; U.S. Pat. No. 3,792,108, issued Feb. 12, 1974; U.S. Pat. No. 3,872,180, issued Mar. 18, 1975; and British Patent Specification No. 1,128,091, published Mar. 16, 1966. Among the catalysts that have been developed for the reaction of olefins with ethylene include inorganic refractory materials containing molybdenum and/or tungsten oxide.
Several patents disclose the use of promoter to enhance the catalyst activity. Elemental metal promoters selected from the group consisting of barium, magnesium, tungsten, silicon, antimony, zinc, manganese and tin are disclosed in U.S. Pat. No. 4,568,788, issued Feb. 4, 1986, U.S. Pat. No. 4,522,936, issued June 11, 1985, U.S. Pat. No. 4,524,235, issued June 18, 1985 and U.S. Pat. No. 4,629,719, issued Dec. 16, 1986. In addition, organometallic compounds, such as aluminum and tin alkyls to promote solid catalysts including molybdenum and rhenium oxide for the disproportionation are disclosed in U.S. Pat. No. 4,454,368, issued June 12, 1984 and U.S. Pat. No. 3,829,523, issued Aug. 13, 1974.
It has been found that alpha olefins having internal contaminants can be purified by a process which comprises contacting the contaminated alpha olefin feed with an organoborane promoted catalyst comprising an alkali metal doped molybdenum and/or rhenium oxide supported on an inorganic oxide support. During the process, the contaminated olefin feed is reacted with ethylene in the presence of the catalyst. The alpha olefins present undergo degenerate metathesis (ethenolysts) and are thus unchanged, whereas the internal olefin contaminants are converted to alpha olefins having a lower carbon number. This chemical transformation of the internal olefin contaminants to alpha olefins results in high purity alpha olefins as well as minimizes potential side reaction, such as self-metathesis and double bond isomerization.
It is therefore an object of this invention to provide a process for the purification of alpha olefins containing internal olefin contaminants. It is further an object of this invention to convert the internal olefin contaminants in the alpha olefin feedstock to alpha olefins having lower carbon numbers. Another object is to provide a catalyst system adapted for high efficiency reaction and high selectivity to alpha olefin production from internal olefins and ethylene. The catalyst system is required to convert the internal olefin contaminants to alpha olefins without significant olefin isomerization and ethylene polymerizations.
The present invention is therefore directed to a method of purifying alpha olefins, particularly to a method of removing internal olefins from alpha olefins.